Generator armature



Jan. 15, 1935. H. GROB 1,988,039

GENERATOR ARMATURE Filed July 18, 19:52

V H. Gro

IN VEN TOR.

A TTORNEYS.

Patented Jan. 15, 1935 UNITED STATES GENERATOR ARMATURE Hugo Grob,Berlin, Germany Application July 18, 1932, Serial No. 623,205 In GermanyJuly 13, 1931 1 Claim.

This invention relates to high-speed direct current generators and hasfor its object to provide means for removing or at least diminishing theundesired influence of the remanent magnetism 5 of the iron parts of thegenerator,

In all direct current generators the influence of the remanent magnetismof the iron parts entails the disadvantage that the voltage supplied bythe generator when starting is too low and reaches its regular valueonly once the generator is working under full load whereby, due to theeffect of the compound winding, the full excita tion has becomeeffective. This drawback must be avoided as far as possible ingenerators which are intended for supplying a uniform voltage which isindependent of the load.

This undesired effect of the remanent magnetism can be diminished, asknown, by inserting an additional magnetic resistance into the magneticcircle. This additional resistance necessitates a corresponding increaseof the exciting ampere-turns in relation to the magnetomotiveforce ofwhich the magnetomotive force of the remanent magnetism falls toinsignificance.

The said additional resistance can be placed either in the air-gap, inthe yoke of the generator, or in the teeth of the armature. As will beseen from the following the first named two places, however, are notadapted to produce the desired effect. If the additional magneticresistance is produced by an increase of the air-gap between thearmature and the pole-shoes, the self-excitation of the generatorbecomes difiicult; if the additional resistance is placed in the casingby diminishing the cross sectional area of the yoke the remanentmagnetism of the generator increases because in consequence of thediminishing of the cross sectional area of the yoke the restricted partof the yoke becomes saturated to a higher degree. Besides, therestriction has to be machined very exactly, because even a slightunintentional further reduction of this cross section causes themagnetic resistance to increase rapidly.

If, however, the additional resistance is provided in the armatureteeth, these drawbacks are Wholly overcome. Due to the permanentreversal of magnetism during the revolution of the armature no increaseof the remanence will occur and also the self-excitation of thegenerator is not affected.

For a suflicient suppression of the undesired efiect of the remanencethe additionally inserted magnetic resistance must have a certain value.In high-speed direct current generators, to which the present inventionrelates principally, for instance, in generators which are driven bysteam turbines, the radial length of the slots is rather short, becauseonly a relatively small volume of copper is necessary for the armaturewinding. In consequence thereof the teeth are also rather short and ifthe additional magnetic resistance is produced by diminishing the crosssection of the teeth, this will necessitate a high saturation, the exactvalue of which, owing to the great influence of even a small deviationof the dimensions or of the magnetic quality of the iron, is verydifiicult to attain.

The object of the present invention is a shape of the slots of thearmature of a high-speed direct current generator which gives thearmature teeth such a length that it is possible to place into the samethe additional magnetic resistance without being compelled neither totoo high a saturation nor to an extreme accuracy in the dimensions. Thisattained by enlarging the slot space in radial direction toward thecentre of the armature, this space then becoming considerably largerthan is necessary for placing the armature winding. As then therestricted part of the magnetic circle is longer, the saturation of thispart necessary to produce the additional magnetic resistance need not beso high, and therefore admits a more exact calculation. Besides,inaccuracies in the dimensions or in the magnetic quality of the iron donot influence the saturation to a great extent.

In the accompanying drawing the figure is a diagrammatic view of anexample of the slot construction according to this invention.

A is the armature plate with the slots B. These slots are made deeperthan is necessary for placing the winding C in order to make sure thatthe tooth-length a is sufiicient to produce the required additionalmagnetic resistance. The slotspace not occupied by the winding C isfilled up with insulating material E or with another nonmagneticmaterial.

By the enlargement of the slots, the iron-losses in the teeth aresomewhat increased. As, however, the tooth-iron-volume is rather smallin high-speed generators, these losses are only of little account; theycan, moreover, easily be compensated by increasing the crossection ofthe winding for which there is sufficient space seeing that the slotspace is designed considerably larger.

For better commutation the armature conductors usually are arranged asnear as possible to the armature-surface.

To recapitulate the invention: In high-speed direct current generatorsit is advantageous, unless special conditions have to be considered, tomake the slots as small as possible, just sufficient for placing thewinding in order to attain a free and strong magnetic flux. The presentinvention, however, demonstrates that by increasing the slots it ispossible to avoid the disadvantages of the remanent magnetism withoutaffecting the self-excitation. The idea of the invention is to enlargethe slots just enough for keeping down the efiect of the remanencesufiiciently, but not more, so that the required number of ampereturnsand the additional tooth-iron-losses do not become too high.

It is acknowledged that it has been known heretofore to provide a smallspace around the conductors for insulation purposes or for mechanicalreasons; e. g. for facilitating the embedding of the winding.

The invention may also be used in the case of alternating currentgenerators provided with a direct current collector, the purpose ofwhich is the excitation of the generator.

I claim:

Means for reducing the remanent magnetism of a high speed direct currentcompound generator comprising a slotted armature having conductorsarranged in the slots, the armature teeth being proportioned to producea magnetic reluctance sufficient to effect the desired reduction inremanent magnetism, the slots being thereby enlarged beyond thenecessary size and a member of 20 non-magnetic material for filling theexcess slot space.

HUGO GROB.

